The invention relates to a pump assembly comprising: an electric drive motor having a stator and a rotor designed as a permanent magnet rotor; at least one impeller connected to the rotor via a rotor shaft; a thrust bearing designed such that it accommodates the axial forces acting on the impeller and the rotor shaft upon operation of the pump assembly; and at least one radial bearing arranged on the rotor shaft.
Pump assemblies are particularly known as heating circulation pump assemblies, which form a construction unit of a pump and an electric drive motor. The electric drive motors are often designed as permanent magnet motors, I.e., they comprise a permanent magnet rotor which rotates in the inside of a stator. At least one pump impeller which rotates in a pump housing, is connected to this permanent magnet rotor via a rotor shaft. On operation of the pump assembly, an axial force acts on the shaft, and this axial force is accommodated by a thrust bearing on the rotor shaft or the rotor.
These pump assemblies are designed as wet-running pump assemblies, I.e., the rotor runs in the inside of a can or canned pot in the fluid to be delivered. The bearings which mount or support the rotor or rotor shaft, as a rule are lubricated by the fluid to be delivered. With these pump assemblies, during longer periods of standstill, there exists the problem that contamination, which is contained in the fluid to be delivered, causes the bearings to become stuck, so that the motor can no longer start up due to a starting moment which is too low.